The invention relates to a device in a road or rail vehicle for determining a vertical distance between a vehicle body and at least one vehicle wheel which is adjustably mounted thereon.
DE 31 34 115 C2 presents an air suspension system, in particular for motor vehicles, which has a wheel or axle level controller in which [lacuna] are activated directly or by means of piezoelectric, capacitive-electric or inductive-electric pressure elements and solenoid pressure control elements starting from a predefined deceleration value by means of a signal transmitter which brings about the control of the air pressure of, in each case, one air suspension element or of the air pressure of all the air suspension elements, is based on mass inertia and acts parallel to the underlying surface, which pressure elements and solenoid pressure control elements produce restoring moments by means of spring stiffening in order to maintain the vehicle at a certain level. The intention is that this air suspension system is to be used to compensate the changes in level which occur when the vehicle is operating when it is braking in a straight line, on a bend and when braking during cornering.
DE 196 45 897 A1 discloses a vehicle which has at least four vehicle wheels which are mounted on a vehicle body so as to be sprung in relation to it and have inflatable tyres. The known vehicle also has a device of the type mentioned at the beginning, each vehicle wheel being assigned a position sensor with which the distance between the respective vehicle wheel and the vehicle body can be determined. In the known vehicle, distance signals which are generated by the position sensors and are correlated to the distance values are used to detect an incorrect tyre pressure, for which purpose it is checked whether, averaged over time, the vehicle wheels lie approximately in a common plane.
However, usually a device of the type mentioned at the beginning is used for adjusting the level of the vehicle body in relation to the underlying surface on which the vehicle is located, appropriate level adjustment elements being assigned to the respective vehicle wheels. A level adjustment system is used, for example, to set continuously a constant distance between the vehicle body and underlying surface irrespective of the vehicle loading. Such a level control system produces advantages in the structural configuration of the spring stiffness of the vehicle suspension system. The constant ground clearance also results in constant camber values and toe angle values at the vehicle axles, said values being independent of the vehicle loading, which results in improved dynamic properties.
In addition, a level adjustment system can be used to set, within certain limits, any desired level of the vehicle body either arbitrarily or as a function of parameters. Such a level adjustment system can cause the level of the vehicle to be lowered, for example at high vehicle velocities, in order to reduce the aerodynamic drag. Likewise, there may be provision for the driver to raise the level of the vehicle on a poor underlying surface, in order to increase the ground clearance of the vehicle.
Furthermore, a level adjustment system can also be used to align the vehicle body parallel to the underlying surface independently of the respective loading state of the vehicle. In this context, the vehicle body can be aligned horizontally with respect to a longitudinal axis of the vehicle and/or with respect to a transverse axis of the vehicle. This parallel alignment of the vehicle body, also referred to as xe2x80x9clevellingxe2x80x9d, relative to the underlying surface ensures that the vehicle is always in an optimum position when the vehicle is loaded asymmetrically. For example in the case of a passenger car, this makes it possible to ensure that dipped headlights always have an optimum, in particular non-dazzling, beam path.
Level adjustment devices can be restricted here to individual axles of a vehicle (for example rear-axle level adjustment) or relate to all the axles of the vehicle (for example all-round level adjustment).
The devices of the type specified at the beginning which are used in known level adjustment devices have actual value sensors which register the distance between the vehicle wheel and the vehicle body. Such an actual value sensor can be embodied, for example, as an inductive linear travel sensor or as a hydraulic or electric rotational angle sensor and is then coupled, in the first instance, to the vehicle body and, in the second instance, to a vehicle component (coupling component) which is adjusted, together with the vehicle wheel, relative to the vehicle body. Such a coupling component can be, for example, an axle link of an associated wheel suspension element. In the case of the actual value sensors which are embodied as rotational angle sensors, it is also necessary to have a mechanical transmission element which couples the rotation angle sensor to the coupling component which is to be tapped. For this reason, the known devices of the type mentioned at the beginning are usually of complex design.
The present invention is concerned with the problem of specifying a different expedient embodiment, which has a simplified design, for a device of the type mentioned at the beginning.
The present invention is based on the general idea of using an inclination sensor which is assigned to the vehicle body (vehicle-body-related inclination sensor) to determine an angle of inclination of the vehicle body with respect to a reference position, and to use an inclination sensor which is assigned to the respective vehicle wheel (wheel-related inclination sensor) to determine an angle of inclination of the vehicle wheel or of a coupling component which couples the vehicle wheel to the vehicle body, with respect to a reference position. The current angle of inclination of the vehicle wheel or of a coupling component relative to the vehicle body can then be determined from a combination of the inclination values which are determined for the vehicle body and for the respective vehicle wheel. This angle of inclination of the vehicle wheel and/or of the coupling component with respect to the vehicle body can then be used to determine, for example computationally, the current vertical distance between the respective vehicle wheel and the vehicle body. In contrast to the prior art, in which an actual value sensor is coupled, in the first instance, to the vehicle body and, in the second instance, to the vehicle wheel or the coupling component, in order to measure, by means of relative movements between the vehicle wheel or the coupling component and the vehicle body, a value which is correlated to the vertical distance between the vehicle body and vehicle wheel, the device according to the invention exhibits two inclination sensors, one of which is attached to the vehicle body and the other of which is attached to the vehicle wheel or coupling component, in order to calculate, from the inclination values of the inclination sensors, a value which is correlated to the vertical distance between the vehicle body and the vehicle wheel.
The use of the device according to the invention produces the following advantages for installation in a motor vehicle: because the inclination sensors are attached directly to the vehicle body and to the vehicle wheel and/or to the coupling component, additional transmission elements can be dispensed with, with the result that the number of components and thus the costs and the weight of the device are relatively low. Furthermore, inclination sensors can be of relatively small design, with the result that the necessary installation space for the sensors in the vicinity of the axle casing or wheel casing is low, in particular free travel for the kinematics of a conventional actual value sensor which is coupled to the vehicle body and to the wheel and/or to the coupling component can be dispensed with. In conventional actual value sensors, it has been necessary to carry out a level standardization after their installation in order to compensate installation tolerances when positioning the actual value sensors, and in order to compensate manufacturing tolerances of the actual value sensors. Such a level standardization can be dispensed with when the inclination sensors are used, since the inclination sensors can be standardized in terms of their output signal with adequate precision during manufacture, and because the inclination sensors can be positioned and installed on the vehicle body and on the respective coupling component with sufficiently tight tolerances. Furthermore, the device according to the invention provides the possibility of making available current level information by means of the control unit of the device. This information can then be used, for example, in a workshop or in the final mounting stage of the vehicle, for adjusting and checking the axles, for example for a camber and toe angle adjustment, without an external inclination angle measuring instrument being required, as in the past, to determine the level.
In the invention, the control unit for generating the distance signal from the vehicle-body-related inclination signal and the wheel-related inclination signal forms a differential signal and assigns a vertical distance between the vehicle wheel and the vehicle body to said signal and generates the distance signal which is correlated to this vertical distance. This assignment between the differential signal and vertical distance is preferably recorded in the manner of a characteristic diagram and stored in the control unit. Such characteristic-diagram-type assignments can be implemented easily and have proven invaluable in practice in other technological fields, in particular as a result of their reliability.
The coupling component to which the wheel-related inclination sensor is attached is preferably a constituent part of a wheel suspension system which supports the vehicle wheel on the vehicle body, in particular this component is an axle link, for example a transverse link or a semi-trailing arm axle, or a torsion bar of a torsion-bar suspension system or a torsion bar of a torsion-bar transverse stabilizer. In other words, the wheel-related inclination sensor is attached to a component which is present on the vehicle in any case, with the result that no additional expenditure is required in this respect.
According to one development of the device according to the invention, said device, or its control unit, can be coupled to a level adjustment device of the vehicle or integrated into such a device, said level adjustment device having appropriate level adjustment elements which are each assigned to one of the vehicle wheels. The level adjustment device here processes the distance signals of the control unit and can carry out, as a function thereof, a level adjustment of the vehicle body in relation to an underlying surface, for example road or rail. Depending on how many vehicle wheels are equipped with a wheel-related inclination sensor, and depending on whether a vehicle-body-related inclination signal which is generated by a common vehicle-body-related inclination sensor is used for all the wheel-related inclination signals, or whether a separate vehicle-body-related inclination sensor is provided for each axle, the vehicle-body-related inclination signal of which sensor is used for processing the wheel-related inclination signals which are assigned to the wheels of this axle, it is possible to use the level adjustment device to adjust the vehicle body to a predefined level and/or set the vehicle body to a predefined level and/or align to the vehicle body parallel to a transverse direction of the underlying surface lying in a transverse plane of the vehicle which contains the transverse direction of the vehicle (levelling with respect to the longitudinal axis of the vehicle), and/or to align the vehicle body parallel to a longitudinal direction of the underlying surface lying in a longitudinal plane of the vehicle which contains the longitudinal direction of the vehicle (levelling with respect to the transverse axis of the vehicle).
Further important features and advantages of the device according to the invention result from the subclaims, from the drawings and from the associated description of the figures with reference to the drawings.
Of course, the features which are mentioned above and those which will be explained below can be used not only in the respectively specified combination but also in other combinations or in isolation without departing from the scope of the present invention.